1. Field of the Invention
The present invention relates to an automotive alternator mounted with a stator having a stator core in which slots are formed at a ratio of two per phase per pole.
2. Description of the Related Art
Generally, an automotive alternator includes: a stator composed of a stator winding installed in a cylindrical stator core in which slots extending axially are formed at an even angular pitch in a circumferential direction; and a rotor having a field winding disposed on an inner circumferential side of the stator. The slots are disposed in the stator core at a ratio of one per phase per pole, in proportion to the number of phases in the stator winding and the number of magnetic poles in the rotor.
When the slots are disposed at a ratio of one per phase per pole in this manner, the amount of time that any given tooth formed between the slots overlaps an adjacent pair of the magnetic poles relative to a radial direction is long, leading to increased magnetic flux leakage. This magnetic flux leakage reduces effective magnetic flux and gives rise to surges in the magnetic flux, resulting in fluctuations in the generated voltage and disturbing the output waveform, which causes ripples when the alternating current is converted into direct current.
Thus, an attempt has been proposed in Japanese Patent Laid-Open No. HEI 4-26345, for example, to reduce magnetic flux leakage by disposing the slots at a ratio of two per phase per pole to shorten the amount of time that any given tooth overlaps an adjacent pair of the magnetic poles.
FIG. 9 is a schematic diagram in which part of a first stator such as that described in Japanese Patent Laid-Open No. HEI 4-26345, for example, is developed into a plan.
In FIG. 9, a stator core 60 is composed of a magnetic steel plate formed into a cylindrical shape, slots 61 extending axially being disposed therein at an even angular pitch in a circumferential direction at a ratio of two per phase per pole. Here, for twelve magnetic poles in a rotor (not shown), seventy-two slots 61 are disposed in the stator core 60 so as to obtain a stator winding 63 composed of first and second three-phase alternating-current windings. The seventy-two slots 61 are disposed at a pitch corresponding to an electrical angle of 30xc2x0 from each other, being arranged in order of an a-phase slot 61a, a d-phase slot 61d, a b-phase slot 61b, an e-phase slot 61e, a c-phase slot 61c, and an f-phase slots 61f repeatedly in a circumferential direction.
An a-phase winding phase portion 63a is constructed by winding conductor wires into a wave shape in the a-phase slot group 61a, a b-phase winding phase portion 63b is constructed by winding conductor wires into a wave shape in the b-phase slot group 61b, and a c-phase winding phase portion 63c is constructed by winding conductor wires into a wave shape in the c-phase slot group 61c. The first three-phase alternating-current winding is constructed by forming the a-phase, b-phase, and c-phase winding phase portions 63a, 63b, and 63c wound in this manner into a Y-connection (an alternating-current connection). Here, the a-phase, b-phase, and c-phase slots 61a, 61b, and 61c into which the a-phase, b-phase, and c-phase winding phase portions 63a, 63b, and 63c are inserted have a phase difference corresponding to an electrical angle of 120xc2x0 from each other.
A d-phase winding phase portion 63d is constructed by winding conductor wires into a wave shape in the d-phase slot group 61d, an e-phase winding phase portion 63e is constructed by winding conductor wires into a wave shape in the e-phase slot group 61e, and an f-phase winding phase portion 63f is constructed by winding conductor wires into a wave shape in the f-phase slot group 61f. The second three-phase alternating-current winding is constructed by forming the d-phase, e-phase, and f-phase winding phase portions 63d, 63e, and 63f wound in this manner into a Y-connection. Here, the d-phase, e-phase, and f-phase winding phase portions 63d, 63e, and 63f have a phase difference corresponding to an electrical angle of 120xc2x0 from each other. Furthermore. the d-phase, e-phase, and f-phase winding phase portions 63d, 63e, and 63f have a phase difference corresponding to an electrical angle of 30xc2x0 from the a-phase, b-phase, and c-phase winding phase portions 63a, 63b, and 63c, respectively.
A stator is prepared by installing these six winding phase portions 63a, 63b, 63c, 63d, 63e, and 63f in the stator core 60. In an automotive alternator constructed in this manner, alternating-current outputs from the first and second three-phase alternating-current windings are each rectified by separate rectifiers, and then the rectified outputs are combined.
Thus, because the slots 61 are disposed at a ratio of two per phase per pole, portions of a tooth 62 overlapping an adjacent pair of the magnetic poles relative to the radial direction are dramatically reduced. Hence, magnetic flux leakage is reduced, enabling reductions in effective magnetic flux to be suppressed. Similarly, the generation of surges in the magnetic flux is suppressed, reducing fluctuations in the generated voltage and disturbances to the output waveform, thereby reducing ripples when the alternating current is converted into direct current.
In automotive alternators of the above construction, because the slots 61 of the stator are formed at a ratio of two per phase per pole, the number of slots 61 is greater than when the slots are formed at a ratio of one per phase per pole, giving rise to the following problems:
a) As shown in FIG. 10, a circumferential dimension (L) of the slots 61 is small, becoming 2d greater than L in relation to a radial dimension (d) of conductor wires 64, resulting in the conductor wires 64 being housed in the slots 61 at random, thereby making the space factor of the conductor wires 64 in the slots 61 low and the ratio occupied by a space portion high, and since there are also few contacting portions between the teeth 62 and the conductor wires 64 or contacting portions among the conductor wires 64, heat transfer from the conductor wires 64 to the stator core 60 or from one conductor wire 64 to another is low, making temperature increases in the stator winding 63 high, thereby leading to declines in output and declines in heat durability;
b) Because width dimensions of the teeth 62 are reduced, reducing the rigidity of the teeth 62, electromagnetic noise generated by the teeth 62 due to circumferential vibrations is increased;
c) Because circumferential dimensions of the opening portions 65 of the slots 61 are small, the frequency with which the conductor wires 64 come into contact with flange portions 67 of tip portions of the teeth 62 when the conductor wires 64 are installed from radially inside toward the outside increases, making electrical insulation of the conductor wires 64, which are coated with an electrical insulator, poor; and
d) Because gaps arise easily between wedges 66 and the conductor wires 64 on the radially innermost side, and because circumferential projection portions on the flange portions 67 for hooking the wedges 66 are small, there is a risk that the wedges 66 will oscillate and dislodge from the opening portions 65.
The present invention aims to solve the above problems and an object of the present invention is to provide an automotive alternator capable of reducing the magnitude of temperature increases and electromagnetic noise in a stator.
In order to achieve the above object, according to one aspect of the present invention, there is provided an automotive alternator including:
a rotor fixed to a shaft rotatably supported in a case; and
a stator provided with:
a cylindrical stator core supported in the case so as to envelop the rotor, slots extending axially being formed in the stator core so as to line up in a circumferential direction at a ratio of two per phase per pole; and
a stator winding constructed by installing a conductor wire coated with an electrical insulator in the stator core,
a relationship between a radial dimension (d) of the conductor wire coated with the electrical insulator and a circumferential width dimension (L) of the slots being 2d less than L.
A cross section of the slots taken along a radial direction may have a rectangular shape.
A width dimension (s) of an opening portion of the slots may be 1.5 or more times a radial dimension (d) of the conductor wire.
An inner circumferential corner portion of a radially-wide flange portion on a tip portion of a tooth between the slots may have a curved shape.
An electrically-insulating resin layer may be formed on an inner wall surface of the slots.
First and second three-phase alternating-current windings may be constructed by installing a plurality of the conductor wires in the slots, a predetermined number of the conductor wires being bundled together.
A deforming cylindrical plug may be disposed inside an opening portion of the slots.
A deforming hollow cylindrical plug may be disposed inside an opening portion of the slots.
A deformable plug may be disposed inside an opening portion of the slots.
A cut portion may be formed in the plug.
Shapes of first and second circumferential end portions of the flange portion may be asymmetrical.
A varnish portion may be disposed on an inner circumferential side of the plug.